This study examined the association among three conceptualizations of work-related rumination (affective rumination, problem-solving pondering, and detachment) with sleep quality and work-related fatigue. It was hypothesized that affective rumination and poor sleep quality would be associated with increased fatigue and that problem-solving pondering and detachment would be associated with decreased fatigue. The mediating effect of sleep quality on the relationship between work-related rumination and fatigue was also tested. An online questionnaire was completed by a heterogeneous sample of 719 adult workers in diverse occupations. The following variables were entered as predictors in a regression model: affective rumination, problem-solving pondering, detachment, and sleep quality. The dependent variables were chronic work-related fatigue (CF) and acute work-related fatigue (AF). Affective rumination was the strongest predictor of increased CF and AF. Problem-solving pondering was a significant predictor of decreased CF and AF. Poor sleep quality was predictive of increased CF and AF. Detachment was significantly negatively predictive for AF. Sleep quality partially mediated the relationship between affective rumination and fatigue and between problem-solving pondering and fatigue. Work-related affective rumination appears more detrimental to an individual's ability to recover from work than problem-solving pondering. In the context of identifying mechanisms by which demands at work are translated into ill-health, this appears to be a key finding and suggests that it is the type of work-related rumination, not rumination per se, that is important.